Received 19 September 2013Accepted 27 October 2013Published online 06 November 2013

Acknowledgments:

This work was supported by the German science foundation (DFG) via the German priority program SPP 1386 “Nanostructured Thermoelectrics” and SPP 1666 “Topological Insulators,” as well as within the Graduiertenkolleg 1286 “Functional Metal-Semiconductor Hybrid Systems.” We thank L. Akinsinde and R. Meißner for technical support.